1. Field of the Invention
This invention relates to a plasma apparatus capable of changing the distribution of generated plasma.
2. Description of the Related Art
In manufacturing a semiconductor integrated circuit, for example, plasma is used to accelerate ionization or chemical reaction of treatment gases in ashing, etching, CVD (Chemical Vapor Deposition), etc. A high frequency induction system using a spiral antenna is known as a method for generating such plasma.
As is described, for example, in European Patent Application No. 379,828, in the high frequency induction system, that surface (the upper surface, in general) of a chamber which is opposed to a wafer chuck is made of an insulator such as quartz glass, and a spiral antenna is secured to an outer wall surface of the chamber. A high frequency current is flown through the chamber to form a high frequency electromagnetic field, thereby causing electrons flowing through the electromagnetic fields to collide with neutrons of a treatment gas, ionize the gas and generate plasma.
Further, to precisely and widely control the region in which plasma is generated, it has been proposed that the spiral antenna is divided into two antenna elements, and a high frequency power is applied to each antenna element.
The thus-generated plasma is used in a discharge process for discharging the electricity accumulated on the wafer chuck, in a cleaning process for cleaning the walls of the chamber, and in an etching process.
Since the discharge process, the cleaning process and the etching process require plasma of different distributions, it is necessary to create plasma of an optimal distribution in each process.